Constant flexure stress energy storing beam

ABSTRACT

A flexural energy storing beam for use with punching and printing hammers in computers and high speed data processors, said beam having a contour optimized according to the energy input whereby in the bending of the beam the maximum principal stress is constant at every cross section of the beam.

I ,7 United States Patent 1 1 1 3,742,800 Frohrib July 3, 1973 1CONSTANT FLEXURE STRESS ENERGY [56] References Cited STORING BEAM UNITEDSTATES PATENTS [7 Inventor: Darrell A. Frohrib, St. Paul, Minn.2,599,036 6/1952 Efromson et at. ..'310/2 7 2,838,700 6/1958 Bii ard310/27 1 ASSIgneeI T Regents f the University of 2,999,632 9/1961 Taiileur 234/109 Minnesota. ap M 3.055,:50 9/1962 Hubbard 83/587 x3,123,290 3/1964 Rabinow et a1 234/1 15 [22] 1972 3,453,919 7/1969 Ehratet a1. 83/589 [2]] Appl. No.: 216,740

Primary Examiner-Frank T. Yost Related US. Application Data Alto ne-Robert W. Gutenkauf et a1. [63] Continuation-impart of Ser. No. 53,538,July 9, 1970, r y

abandoned. [57] ABSTRACT [52] Us. Cl D 83/587 83/575 83/597 A flexuralenergy storing beam for use with punching 234/lO9 310/27 and printinghammers in computers and high speed [51] Int Cl 826d g B2621 5/08 i U02data processors, said beam having a contour optimized [58] Field aiSearch 83/587 586 57s accmding the energy input whereby bending of thebeam the-maximum principal stress is constant at every cross section ofthe beam.

6 Claims, 5 Drawing Figures CONSTANT FLEXURE STRESS ENERGY STORING BEAMCROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION Inthe field of computers a wide variety of printing and punching devicesare used as peripheral equipment for the printing and punching ofcomputer cards or tape or the like. Computers and data processors areable to electronically feed data or other output signals at a ratesubstantially faster than the mechanical components of the peripheralequipment can be reliably actuated to record this output. Thus, apractical limitation is imposed upon the utilization of computers andhigh speed data processors by the speed of operation of the printing andpunching mechanisms.

Generally, a printing or punching device can incorporate an impactelement such as a print hammer or a punch key, biasing means, and meansfor holding the impact element against the urging of the biasing means.At the proper moment the holding means is released, and the energystored by the biasing means is translated into kinetic energy of theimpact element, enabling it to perform its impact function. Reduction inthe size and the number of moving parts of a printing or punchingmechanism generally results in a device having an increased speedcapacity and greater reliability, for example the flexure spring punchof the U. S. Pat. No. 3,144,988.

It has been recognized as extremely advantageous to employ flexureelements as the biasing means for the loading of a print hammer or punchkey or other impact element, thereby avoiding troublesome abradingmechanisms such as cams, helical springs, abrading pivots, and the like,for example see U. S. Pat. Nos. 3,460,753 and 3,447,455. Commonly, m'anyconventional printing and punching devices store flexural energy in aflexural bundle comprised of one or more parallel slender beamsconnected at one end to a supporting frame and at the other end to anend mass, for example the print hammer unit of U. S. Pat. No. 3,359,921.To the mass is attached the printing or punching element, or otherimpact element to perform the desired impact function as, for example,in a wheel type printer where a hammer presses the paper against a wheelhaving print characters positioned along its periphery. Means areprovided to deflect the mass, thereby deflecting the beams in a bendingconfiguration and effecting the storage of flexural energy. Upon therelease of the mass, the flexural energy stored in the beams istranslated into kinetic energy enabling the impact element, upon impact,to perform the desired impact function. The flexural means are calledupon for the storage and release of energy under high frequency impactconditions. Flexure beams of uniform cross section capable ofwithstanding such demanding use are inconveniently bulky and henceslower acting and not susceptible of the high speed operation capabilityof modern-day computers and data processors.

Typically, a flexure member is constituted as a slender beam of uniformtransverse cross section. Upon deflection of such a beam in a bendingconfiguration, the end forces and moments acting on the beam introduceunequal, non-uniform stress along the length of the beam. Therefore,many sections of the beam are loaded to stress levels considerably belowpermissible design stresses. This results in excessive material volumefor a prescribed flexural energy level over much of the length of thebeam. The necessity of flexing this excessive material results inexcessive power needs in the flexing means and in slower operatingcycle-times in the printer.

SUMMARY OF THE INVENTION The invention relates to an improved impactoutput device such as a printing or punching head (for peripheral use,for example, with computers and high speed data processors) of the typeactuated by flexural energy storing beams comprising a flexure bundle,connected cantileverly to a parent structure at one end and supportingat the other end an end mass including an impact element such as a printhammer or punch key. In particular, the invention relates to an improvedflexure beam having a contoured profile matched to an energy input inthe form of a transverse load acting at a prescribed location on theflexure bundle. The profile of the beam is matched to the energy inputso that under the prescribed loading conditions the maximum principalstress induced by.the loading is virtually constant at all crosssections along the beam and occurs at the extreme outer fibers of thebeam. Consequently less material is required for each flexure beam andthe effective end inertia contributed by the beams is reduced to lessthan 50 per cent of that contributed by uniform flexure beams of uniformcross section. This reduction allows an increased cycling speed of theprinting or punching operation, requires less power to flex the bundle,and causes less fatigue on the beams of the flexure bundle.

An object of the invention is to provide a flexure beam which underprescribed load conditions will have a constant maximum principal stressat every cross section along its length. A further object of theinvention is to provide an optimized flexure beam structure for use inperipheral equipment with computers and high speed data processors, forexample. A further object of the invention is to provide a flexural beamof reduced material volume and capable of higher operating frequencies.Further objects will become apparent upon the following description.

IN THE DRAWINGS FIG. 1 is an elevational view of a computer punch headof the invention including a diagrammatic representation of a bundle offlexure beams of the invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is an enlarged diagrammatic view of one of the flexure beams ofFIG. 1;

FIG. 4 is a side elevation of a generalized slender beam in a bendingconfiguration to illustrate the deflections of the beam and the endforces acting upon the beam; and

FIG. 5 is a side elevation of the beam of FIG. 4 separated from the endmass to further illustrate the end forces acting on the beam and on theend mass.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,there is shown in FIG.

l a punch head, indicated generally at 10, having an end mass 11. Equallength flexure beams 16, comprising a flexure bundle, are cantileverlyattached at one end to a parent structure and support at the other endthe mass 11. The flexure beams 16 of the invention are diagrammaticallyshown to have an optimized profile contour, as will be more fullydescribed herein. As seen in FIG. 2, the flexure beams 16 are of uniformtransverse horizontal dimension. On one side the end mass 11 has an arm13 extending inwardly toward the parent structure 15. On the arm 13 islocated a first set of electromagnetic contacts 14. In alignment toreceive the contacts 14 when the bundle is deflected and spaced apartfrom the contacts when the beams 16 are in an undeflected configuration,is a second set of stationary electromagnetic contacts 17 which aresecured to an extension of the parent structure 15 as part of anelectromagnet 51. Upon energizing the electromagnet, there is created anelectromagnetic attracting force, represented by the vector 18, betweenthe first contacts 14 and the second contacts 17, which causes the endmass 11 to be deflected to and retained in a position where the two setsof contacts meet. In such a deflected state, the flexure beams 16 are ina bending configuration thereby storing flexural energy. For the reasonswhich will presently become apparent, in the embodiment of the inventionas shown, the first set of contacts 14 are located on the arm 13 in aposition such that the centroid of the attracting force 18 acts in ageometric plane which passes through'the flexure beams 16 at a pointone-third the length of the flexure beams 16 measured from the end masstoward the parent structure.

On the side of the mass 11 opposite the contacts 14 is a punch hammer12. In punching alignment with the punch hammer 12 are computer cardfeeding and holding means, which do not form a part of the presentinvention, but which include a punching die 19, a stripper die 20 andfeed rollers 21. A computer card 22 rests on the punching die 19 betweenthe punching die 19 and the stripper die 20.

One of the flexure beams 16 of the invention is more particularlydiagrammatically illustrated in FIG. 3. The beam has a profile contouroptimized so that when flexure force is applied as shown in FIG. 1 themaximum principal stress is the same magnitude at every transverse crosssection of the beam. The beam has an axial length I measured along thecenter line 27 of the beam between the point 28 where the flexure beamis attached to the end mass 1 l and the point 29 where the beam isattached to the parent structure 15. The beam has a transverse verticaldimension or thickness t which varies along the length l of the beamaccording to the optimized profile contour of the beam. For conveniencethe parameter t llis designated by the term I}. A parameter x is definedas the distance starting at the point 28 along the center line 27 towardthe point 29 and J? is defined as said distance x divided by the lengthl. The functional relationship between I, and i is represented as thethickness function, f, (it). The thickness of the beam end attached tothe parent structure at i l is represented as t], (l). The profile of abeam is then described by the following profile equations:

0 )50 3 l/2) in the region 76+ As isl 0 D/ n (l) (1 3 i/Z) in the region0 s is /aA 4 t], (i)/i,, (l) (3 A/Z) in the region A:- A '5 22 /:3+Awhere The beam profile provided by the profile equations results inabrupt contour changes in the profile at the points x 0, rs-A, AHA,and 1. At these points of discontinuity there will arise stressconcentrations. Such stress concentrations may be alleviated byany ofseveral known engineering methods. For example, the addition of fillets30, 31, 32 and 33 will relieve the'stress concentrations at i 0 and i 1.At the points 30 and 31, fillets having a radius of t", (I), and at thepoints 32 and 33 fillets having a radius of t", (0) will adequatelyrelieve the stress concentration and will require the addition of verylittle material. In the region I? Ar-A to X zz+A the addition of fillets34, 35 having a radius of 2 A to smooth the profile in that region willadequately relieve the stress concentrations and will require theaddition of very little material.

The derivation of the profile equations is best seen by considering FIG.4 where there is shown a normally straight slender beam 36 in a bendingconfiguration below the yield stress so as to follow I-lookes law; Thedeflection of the beam 36 is exaggerated for purposes of illustration.The beam is cantileverly attached at one end to a parent structure 37and at the other end to an end mass 38. It is understood that the beam36 is one of a plurality of equal length beams attached at one end tothe end mass 38 and to the parent structure 37 at the other end, inparallel relationship as the beams 16 of the flexure bundle of FIG. 1.The center line of the beam 36 in the deflected state is represented bythe line 39, and in the undeflected state by the line 40. The beam hasan axial length l which is measured along the center line from the point41 to the point 42. For convenience, a parameter x is defined as thedistance along the center line 39 from the point 41 toward the point 42.In the deflected state there is acting on the beam. at the end x 0, endloads comprising a shear force F,,, represented by the vector 43, and abending moment M represented by the vector 44. The shear force 43 andthe bending moment 44 are more fully illustrated in FIG. 5 where the endmass 38 is shown separated from the beam 36. There is a reaction force,shown by the vector 53, and a reaction moment, shown by the vector 54,acting on the end mass 38 at the point of attachment of the beam 36. Asseen in FIG. 4, each point on the beam center line in the deflectedstate is displaced from its position on the undeflected center line 40in a direction perpendicular to the center line 40, by a distance whichis designated the displacement v, for an arbitrary point i on the beamcenter line. The displacement v, varies with the position of the pointalong the center line, so that it is expressed as functionally relatedto x, as v, (X). The displacement of the end point 41 of the beam isrepresented by the distance 45 and is, for convenience, termed v. Inaddition, at each arbitrary point i on the beam center line 39, thecenter line is at an angle relative to the undeflected center line 40,which is designated for convenience 0,. Likewise, as the angle 0, variesalong the center line according to the position of the point i, afunctional relationship may be expressed, as 0,(X). The deflection angleat the end point 41 of the beam is shown as the angle 46 and isconveniently termed 0.

According to the well-known moment-curvature relationship for a beam inbending, the second derivative of the displacement with respect to axialdistance x is equal to the bending moment acting on the beam at the ithsection divided by the product of the modulus of elasticity of the beammaterial and the area moment of inertia of the ith section. This ismathematically expressed as:

I where M is the moment acting at the ith section, E

is the modulus of elasticity, and I(x) is the area moment of inertia atthe ith section. 1(x) is dependent upon the section geometry, hence thethickness function, and varies with x. Double integration of themomentcurvature equation for the beam 36, and satisfaction of theboundary conditions that at x l 6(l)= 0 and V,(l)= 0, yields equationswhich are solved for the end loads F, anclM in terms of the enddisplacements 0 and v as a function of the beam length, moduluselasticity and moment of inertia function. These equations represent theloading for which the optimized profile of the invention will give aconstant maximum principal stress at any cross section of the beam.

The stresses in a beam in bending due to both external bending momentand transverse shear force inputs, for example beam 36, are both tensileand shear. The tensile stress at a cross section acts parallel to theaxis of the beam, the only significant shear component acts in the planeof the cross section of the beam and perpendicular to the principalaxis. The maximum tensile stress in bending occurs at the outer fiber ofthe cross section and may be expressed as a function of the end loadsacting on the beam, M, and F and the cross section geometry. As shownearlier, the end loads M and F are expressed in terms of integrals overthe beam length. As an object of the invention is to define a profilewhereby the maximum principal stress is constant, and assuming for themoment that the maximum tensile stress is the maximum principal stress,the first derivative with respect to x of the tensile stress functionmust equal 0. Having expressed the end loads in terms of integrals overthe beam length, the solution of the first derivative equation yieldsthe following solution for section geometry, in terms of the previousnotation:

('i)/i;( )=(3 r- 1/2 in the region 9i; s x s l and in the region 0 s x sA The solution also yields the following relationship of the end loads:F l/M 3 thus dictating the prescribed loading location of FIG.

The above relationships were derived assuming that the maximum tensilestress was the maximum principal stress. This is true in regionsgoverned by tensile stress, but is insufficient where shear stressgoverns as shown by the 0 thickness property provided by the foregoingrelationships at Y= is. An analysis of the shear forces acting on thebeam shows that the shear stress is of a greater magnitude than thetensile stress in the region A Y s A; A, and the two are equal at thepoints i= /3A and /:;+A, where A and x are as previously defined.Therefore, in order to accommodate the shear stress the above profilerelationships must be modified in the region A: A s T s 9i: A by asegment having a thickness T (3?) (3 A/2) The inclusion of fillets asdescribed and illustrated earlier for the relief of stressconcentrations caused by profile discontinuities results in therelationships governing the profile of the beam 16 as earlier presented.

In the use of the invention, referring to FIG. 1, the electromagnet isenergized, thereby creating the attracting force 18, causing thedisplacement of the end mass 11 to a position where the contacts 14 meetthe contacts 17. The flexure beams 16 are then in a bendingconfiguration and have a stored potential energy in the form of flexuralenergy. There is no unnecessary material on the beams 16 as the maximumprincipal stress along the length of each beam is constant. The

amount of flexural energy stored in the flexure bundle is according tothe function to be performed, and is a design parameter of the flexurebundle and the end mass. The feed rollers 21 guide a card 22 into thedesired position between the punching die 19 and the stripper die 20, inalignment with the punch hammer 12. Upon de-energization of theelectromagnet, the flexural energy in the beams 16 is translated intokinetic energy, and impact is effected by the punch hammer 12 upon thecard 22, leaving the correct perforation. The stripper die 20 holds thecard in position as the punch hammer retracts. Because of the reducedmass of the flexure bundle and the end mass, the punching operation isperformed at a higher frequency than could be previously achieved.

From the derived profile equations, as well as from FIG. 1, it isapparent that the minimum thickness of the beams occurs at the point 1?56., or at a point '26 the length of the beams from the end massattaching end to the parent structure attaching end. The beams of thefiexure bundle, as shown by FIGS. 1 and 2, are disposed in parallelfacing relationship. The beams are optimized according to the thicknessdimension rather than a transverse width dimension. Bending propertiesof a beam are more sensitive to thickness than to width. Optimization ofa beam contour according to thickness is thereby more effective.

While there has been illustrated and described one embodiment of theinvention, those skilled in the art will recognize further applicationsof the invention. For example, the punch hammer 12 could as well be aprint key to perform a printing operation. Also in numerous devices suchas electric typewriters there are required slender members which mustoperate at high frequency, and therefore be of minimum mass but able toabsorb a maximum of energy. In such devices the flexure beam of thepresent invention would find application.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An improved impact output device of the type having an end mass, animpact key attached to the end mass positioned to perform an impactfunction relative to a parent structure, at least two flexural energystoring members attached at one end to the end mass and cantileverlyattached at the other end to said parent structure, and means fordeflecting, holding and releasing said energy storing members to causesaid impact key to perform said impact function, wherein:

said energy storing members are disposed in parallel facing relationshipand each said flexural energy storing member is a slender beam having anoptimized contour profile of varying thickness matched to the energyinput to the beam and having a minimum thickness at a point a the lengthof the beam from the end mass attaching end to the parent structureattaching end whereby the maximum principal stress at all points alongthe beam is the same when said deflecting means is operative to flexsaid beam.

2. The impact output device of claim 1 including:

stress relieving fillets at points of stress concentration on each saidflexural energy storing member.

3. The impact output device of claim 2 wherein the means for deflectingthe flexural energy storing members include:

means for electromagnetically deflecting said beams.

4. An improved impact output device for use with computers and dataprocessors including:

an end mass;

an impact element attached to the end mass in a position to perform animpact function;

at least two flexural energy storing members attached at one end tothe'end mass and at the other end to a parent structure, each saidmember having a contour profile according to the equations:

i; (BU/t (l) (3 35- 1/2) in the region A A x l (EU/t, (l) (l 3 Iii/2) inthe region ofO s x s A A 111(7)]?5 (l)=(3 A/2 in the region A A s x s1A; A and means for deflecting, holding and releasing said energystoring members.

5. The impact output device of claim 4 including: stress relievingfillets at points of stress concentration on each said flexural energystoring member. 6. A flexural energy storing member including:

a slender beam for cantileverly attaching one end to a parent structureand for attachingthe other end to an end mass, said beam having acontour profile of varying thickness optimized according to an energyinput acting on a flexure bundle comprised of at least two of saidmembers, said energy input in the form of a transverse load having acentroid acting in line with a point A: the length of the beam from theend mass attaching end to the parent structure attaching end, said beamhaving a minimum thickness at said point A; the length of the beamwhereby the maximum principal stress along the beam is constant.

@753 UN TED "STATES PA ENT OFFICE CERTIFICATE OF CORRECTION Patent No.,7 ,800 Dated July 5, 1973 'Inventor(s) DARRELL A. FROHRIB It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4 line 1 1/3 -.A f i 2 1/3 A x 15 lower case, not capital Column5, line 9: Equation should read: 7

i oi 9 X B1 (x) ColumnS, line 46: Equation should contain a 7 closingbracket:

Column 5, line "V (1) 0" should be "vi (7) 0- Signed and sealed this 5thday of March 1974 SEAL Attest:

EDWARD M.FLETCHE R,JR. C. MARSHALL DANN 1 Attesting Officer Commissionerof Patents 1 V UNITED STATES PATENT OFFICE r 569 CERTIFICATE OFCORRECTION Patent No. 3 74 2 ,800 Dated July 3, 1973 It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 4 line 1 1/3 5 v a? 5 1/3 A is lower case, not capital Column 5,line 9: Equation should read:

5* v I M 1 01 a x El (X) Column 5, line: 46: Equation should contain a 1closing bracket:

t GED/E; (1) (3 1/2) 1/2 Column 5, line "V (1) 0" should be --V U) 0'.

. Signed and sealed this 5th day of March 1974'.

SEAL Attest:

'EDWARD M.1=LETCHER,JR. C. MARSHALL DANN 1 v Attesting OfficerCommissioner of Patents 1 v

1. An improved impact output device of the type having an end mass, animpact key attached to the end mass positioned to perform an impactfunction relative to a parent structure, at least two flexural energystoring members attached at one end to the end mass and cantileverlyattached at the other end to said parent structure, and means fordeflecting, holding and releasing said energy storing members to causesaid impact key to perform said impact function, wherein: said energystoring members are disposed in parallel facing relationship and eachsaid flexural energy storing member is a slender beam having anoptimized contour profile of varying thickness matched to the energyinput to the beam and having a minimum thickness at a point 1/3 thelength of the beam from the end mass attaching end to the parentstructure attaching end whereby the maximum principal stress at allpoints along the beam is the same when said deflecting means isoperative to flex said beam.
 2. The impact output device of claim 1including: stress relieving fillets at points of stress concentration oneach said flexural energy storing member.
 3. The impact output device ofclaim 2 wherein the means for deflecting the flexural energy storingmembers include: means for electromagnetically deflecting said beams. 4.An improved impact output device for use with computers and dataprocessors including: an end mass; an impact element attached to the endmass in a position to perform an impact function; at least two flexuralenergy storing members attached at one end to the end mass and at theother end to a parent structure, each said member having a contourprofile according to the equations: to (x)/to (1) (3 x - 1/2) 1/2 in theregion 1/3 + Delta < or = x < or = 1 to (x)/to (1) (1 - 3 x/2) 1/2 inthe region of 0 < or = x < or = 1/3 - Delta to (x)/to (1) (3 Delta /2 )1/2 in the region 1/3 - Delta < or = x < or = 1/3 + Delta and means fordeflecting, holding and releasing said energy storing members.
 5. Theimpact output device of claim 4 including: stress relieving fillets atpoints of stress concentration on each said flexural energy storingmember.
 6. A flexural energy storing member including: a slender beamfor cantileverly attaching one end to a parent structure and forattaching the other end to an end mass, said beam having a contourprofile of varying thickness optimized according to an energy inputacting on a flexure bundle comprised of at least two of said members,said energy input in the form of a transverse load having a centroidacting in line with a point 1/3 the length of the beam from the end massattaching end to the parent structure attaching end, said beam having aminimum thickness at said point 1/3 the length of the beam whereby themaximum principal stress along the beam is constant.